The single absorption refrigeration cycle or loop is well known and has been used for many years. In its basic form, it consists of an interconnected absorber, desorber (generator), condenser, and evaporator that use a refrigerant and an absorbent as a refrigerant pair and a heat source to transfer heat between a heat load and a heat sink.
The absorber contacts low pressure refrigerant vapor with a miscible absorbent. Absorption takes place as a result of the mixing tendency of the miscible materials as well as an affinity between the refrigerant vapor and the absorbent and results in the generation of thermal energy which is released to the heat sink. The mixture formed by the absorption process, which is referred to here as the strong solution, is pressurized by means of a solution pump and conveyed via a heat exchanger to the desorber (generator).
The generator (desorber) causes the refrigerant vapor and absorbent to separate as a result of the application of heat. When the absorbent is a nonvolatile material, heating of the strong solution is sufficient to accomplish complete separation of the refrigerant vapor. The remaining absorbent, referred to as a weak solution, is returned to the absorber to again begin the absorption process.
When the absorbent is a volatile material such as water in an ammonia/water refrigerant pair, a rectifier is required to move the last traces of the volatile absorbent (water) from the refrigerant vapor (ammonia). As used here, the term "rectifier" includes all types of fractional distillation equipment used to remove a volatile absorbent from the refrigerant vapor. Rectification results in heat generation as the volatile absorbent condenses to a liquid. The heat from the rectification process is also released to a heat sink. Removal of the absorbent from the refrigerant vapor is essential in that contamination of the refrigerant vapor with absorbent interferes with refrigerant vaporization in the latter refrigerant vaporization step.
After rectification, the vapor passes to the condenser. The condenser condenses the refrigerant vapor to a liquid with the liberation of heat. The hot liquid refrigerant then passes to the evaporator.
The evaporator revaporizes the hot refrigerant liquid at low pressure and temperature with input of heat from the heat load, i.e., from the refrigerator, room, building, or other medium the system was designed to cool. From the evaporator, the refrigerant vapor enters the absorber to again cycle through the process. FIG. 1 illustrates a typical single cycle absorption system. The temperature of the components increases from left to right while pressure increases from bottom to top.
In evaluating the effectiveness of a particular absorption system, a common measure often used is the "coefficient of performance," i.e COP. The coefficient of performance (COP) is defined as the energy transferred at the load in a unit of time divided by the energy provided to the system in the same unit of time. The thermal efficiency (COP) of a single-effect cycle is typically about 0.5 to 0.7.
To improve thermal efficiency, a system having two separate absorption cycles without fluid connection, one operating at higher temperature and pressure and the other operating at lower temperature and pressure, is used. Various heat exchange arrangements of the components of this two or dual cycle system have been used to improve the operating efficiency of the system as is set forth below.
U.S. Pat. No. 2,196,911 discloses the use of two separate ammonia/water cycles in which the high-temperature generator (desorber) was used to directly heat the low-temperature generator; the lower temperature absorber was cooled by directly rejecting its heat to the high-temperature evaporator. U.S. Pat. No. 3,483,710, using a lithium bromide/water solution pair in each cycle, also discloses cooling the lower temperature absorber by rejecting its heat directly to the higher temperature evaporator and, in addition, using the high-temperature condenser to heat directly the low-temperature desorber (generator). However, it does not disclose the use of the high-temperature generator to heat the low-temperature generator.
U.S. Pat. No. 4,441,332 teaches a separate, dual loop system in which a lithium bromide/water refrigerant pair is used for the upper temperature loop and an ammonia/water refrigerant pair is used for the lower temperature loop. The patent teaches that a salt-based refrigerant pair is to be avoided in the lower temperature cycle in order to avoid freezing and crystallization problems. The condenser from the high-temperature loop is in heat exchange relation with the lower temperature desorber. The patent further provides for selectively arranging heat exchange relations between the higher temperature absorber, the higher temperature evaporator, the lower temperature condenser, the lower temperature evaporator, and the lower temperature absorber. U.S. Pat. No. 4,667,485 further improves on this concept by placing the higher temperature desorber, the higher temperature condenser, and the lower temperature desorber in sequential heat exchange relation from a central heat source.
U.S. Pat. No. 4,542,628 discloses the use of the rejected heat from the high-temperature condenser and absorber to heat the low-temperature desorber (generator). The high-temperature condenser heats the desorber directly while the high-temperature absorber heats the desorber indirectly by means of a closed-loop heat exchanger. The high-temperature evaporator is used to cool the low-temperature absorber and condenser.
U.S. Pat. No. 4,732,008 shows a dual cycle system in which the high-temperature condenser supplies heat directly to the low-temperature generator; the high-temperature absorber is used to heat the low-temperature generator by means of a closed-loop heat exchange system. Both the high and low-temperature evaporators provide cooling to the load. U.S. Pat. No. 5,284,029 improves on this arrangement by providing for direct coupling of the high-temperature absorber to the low-temperature generator.
Accordingly, it is an object of the present invention to provide a multiple cycle absorption refrigeration apparatus that is more efficient than prior devices.
Another object of this invention is to utilize the heat rejected by the rectifier in the high-temperature loop of a dual cycle system.
Another object of this invention is to provide a highly efficient system, i.e., a high COP, for a light commercial refrigeration system, e.g., approximately ten refrigeration tons.
A further object of this invention is to reduce the number of components thereby reducing overall system cost.
Another object of this invention is to reduce the operating pressure of the high-temperature loop with respect to double effect systems.
An additional object of the invention is to utilize as much heat as possible from the high-temperature loop in the low-temperature generator.
Another object of this invention is to more effectively use the heat values in the flue gases given off after the initial heating of the high-temperature desorber.
Another object of this invention is to provide system components that are simple and easy to manufacture.
Another object of this invention is to provide machine components that are more efficient in performing absorption machine processing.
Another object of this invention is to provide a simple and effective device for metering equal amounts of liquid into multiple conduits.
Another object of this invention is to provide a uniform refrigerant vapor velocity that affords improved liquid-vapor equilibrium conditions in absorption, desorption and other mass transfer processes.
Another object of this invention is to provide absorption machine components that are more efficient in thermal energy transfer.
Yet other objects of invention will become apparent to those of ordinary skill in the art from consideration of the present disclosure.